Under the microscope, Rickenella fibula is incredibly distinct, since it is covered with long, cylindric cystidia--but to the naked eye, it is a tiny orange mushroom with many look-alikes. If you squint real hard, you will see that the gills run down the stem, which will (theoretically) eliminate many possibilities, including species of Mycena and Marasmius. The fact that it grows gregariously in moss beds is another crucial clue to its identity, and will help to separate it from species of Xeromphalina, which grow in dense clusters (often numbering in the hundreds) on wood.

In the end, however, several tiny orange species with white spore prints are frustratingly similar, including miniature versions of Cantharellus minor, Hygrocybe cantharellus, and others. Most of these look-alikes are a little bit larger than Rickenella fibula, but you may find that a microscope is needed to be sure of your identification.

Description:

Ecology: Possibly saprobic but apparently involved in some sort of mutualism with moss; growing alone, scattered, or gregariously in moss beds; early summer through early winter; widely distributed in North America.

Cap: Up to 1.5 cm across; convex, becoming broadly convex or somewhat centrally depressed; tacky; fairly smooth; the margin lined, inrolled at first and usually remaining so; orange or yellowish orange when fresh, often fading to buff.

Gills: Running down the stem; close or nearly distant; sometimes with cross-veins; whitish or creamy.

Stem: Up to 5 cm long and almost 2 mm thick; more or less equal; dry; very finely hairy; colored like the cap.